1. Field of the Invention
The present invention relates to a vehicle-mounted radio wave radar for detecting a variable such as a distance or relative speed between a host vehicle (radar-loaded vehicle) and a target in front of the host vehicle.
2. Description of the Related Art
There is known a vehicle-mounted radio wave radar for detecting a variable such as a distance or relative speed between a host vehicle and a target, e.g., another vehicle or an obstacle, in front of the host vehicle by using radio waves of the millimeter-wave (EHF) band (60-77 GHz) in which radio wave beams are less attenuated even in foggy or other bad weather and are able to propagate over a long distance.
Examples of such a vehicle-mounted radio wave radar are disclosed in JP, A, 10-79616 and 10-261917.
In the former JP, A, 10-79616, a radome and a housing are employed to provide a structure for enclosing, e.g., an antenna, a high-frequency circuit section for processing a transmitted/received signal in the same high-frequency range as the transmitted/received signal, and a control circuit section for processing the transmitted/received signal in a relatively low-frequency range and performing other required processing. With this structure, the antenna is covered from front by the radome made of a material, such as a resin, which is transparent to electromagnetic waves of the millimeter-wave band with high efficiency, and the remaining part is covered by the housing. The latter JP, A, 10-261917 employs a structure that an antenna, a high-frequency circuit section and a control circuit section are stacked in a housing in this order and fixed to the housing by screws or the likes, and that a ground potential metallic layer is provided between the high-frequency circuit section and the control circuit section.
In the conventional vehicle-mounted radio wave radars described above, ground terminals of the components, i.e., the control circuit section and the high-frequency circuit section, are connected to a ground terminal of a battery remote from the position at which the radar is attached to a vehicle body. The ground terminal of the battery is connected to the vehicle body for grounding. Accordingly, impedance of a certain value depending on wires, body, and other vehicle parts exists between the ground terminals of the control circuit section and the high-frequency circuit section, the ground terminal of the battery, and the vicinity of the position at which the radar is attached to the vehicle body.
The presence of such impedance generates a noise loop through those vehicle parts and may deteriorate the performance of the vehicle-mounted radio wave radar because useless noises and static electricity are applied to the vehicle-mounted radio wave radar.
Further, when the components of the vehicle-mounted radio wave radar are stacked in a housing and fixed to the housing by screws or the likes as disclosed in the latter JP, A, 10-261917, the assembly work is difficult to implement because the housing is usually designed to have the least necessary size just enough to accommodate the components for a size reduction.